Sleep consolidates stimulus-response learning.

Performing a motor response to a sensory stimulus creates a memory trace whose behavioral correlates are classically investigated in terms of repetition priming effects. Such stimulus-response learning entails two types of associations that are partly independent: (1) an association between the stimulus and the motor response and (2) an association between the stimulus and the classification task in which it is encountered. Here, we tested whether sleep supports long-lasting stimulus-response learning on a task requiring participants (1) for establishing stimulus-classification associations to classify presented objects along two different dimensions ("size" and "mechanical") and (2) as motor response (action) to respond with either the left or right index finger. Moreover, we examined whether strengthening of stimulus-classification associations is preferentially linked to nonrapid eye movement (non-REM) sleep and strengthening of stimulus-action associations to REM sleep. We tested 48 healthy volunteers in a between-subjects design comparing postlearning retention periods of nighttime sleep versus daytime wakefulness. At postretention testing, we found that sleep supports consolidation of both stimulus-action and stimulus-classification associations, as indicated by increased reaction times in "switch conditions"; that is, when, at test, the acutely instructed classification task and/or correct motor response for a given stimulus differed from that during original learning. Polysomnographic recordings revealed that both kinds of associations were correlated with non-REM spindle activity. Our results do not support the view of differential roles for non-REM and REM sleep in the consolidation of stimulus-classification and stimulus-action associations, respectively.

Sleep does not aid the generalisation of binocular disparity-based learning to the other visual hemifield.

Visual perceptual learning refers to long-lasting performance improvements on a visual skill - an ability supported by plastic changes in early visual brain areas. Visual perceptual learning has been shown to be induced by training and to benefit from consolidation during sleep, presumably via the reactivation of learning-associated neuronal firing patterns. However, previous studies have almost exclusively relied on a single paradigm, the texture discrimination task, on which performance improvements may rely on higher-order rather than lower-level perceptual skills. In the present study, we tested whether sleep has beneficial effects on a visual disparity discrimination task. We confirm previous findings in showing that the ability to discriminate different disparities is unaffected by sleep during a 12-hr retention period after training. Importantly, we extend these results by providing evidence against an effect of sleep on the generalisation of improved disparity discrimination across the vertical meridian. By relying on a between-subject design, we further exclude carry-over effects as a possible confound present in previous findings. These data argue against sleep as an important factor in the consolidation of a low-level perceptual skill. This sets important constraints on models of the role of sleep and sleep-associated neural reactivation in the consolidation of non-declarative memories.

Anatomic and functional asymmetries interactively shape human early visual cortex responses.

Early visual processing is surprisingly flexible even in the adult brain. This flexibility involves both long-term structural plasticity and online adaptations conveyed by top-down feedback. Although this view is supported by rich evidence from both human behavioral studies and invasive electrophysiology in nonhuman models, it has proven difficult to close the gap between species. In particular, it remains debated whether noninvasive measures of neural activity can capture top-down modulations of the earliest stages of processing in the human visual cortex. We previously reported modulations of retinotopic C1, the earliest component of the human visual evoked potential. However, these effects were selectively observed in the upper visual field (UVF). Here we test whether this asymmetry is linked to an interaction between differences in spatial resolution across the visual field and the specific stimuli used in previous studies. We measured visual evoked potentials in response to task-irrelevant, high-contrast textures of different densities in a comparatively large sample of healthy volunteers (N = 31) using high-density electroencephalogram. Our results show differential response profiles for upper and lower hemifields, with UVF responses saturating at higher stimulus densities. In contrast, lower visual field responses did not increase, and even showed a tendency toward a decrease at the highest density tested. We propose that these findings reflect feature- and task-specific pooling of signals from retinotopic regions with different sensitivity profiles. Such complex interactions between anatomic and functional asymmetries need to be considered to resolve whether human early visual cortex activity is modulated by top-down factors.

Sleep Strengthens Predictive Sequence Coding.

Predictive-coding theories assume that perception and action are based on internal models derived from previous experience. Such internal models require selection and consolidation to be stored over time. Sleep is known to support memory consolidation. We hypothesized that sleep supports both consolidation and abstraction of an internal task model that is subsequently used to predict upcoming stimuli. Human subjects (of either sex) were trained on deterministic visual sequences and tested with interleaved deviant stimuli after retention intervals of sleep or wakefulness. Adopting a predictive-coding approach, we found increased prediction strength after sleep, as expressed by increased error rates to deviant stimuli, but fewer errors for the immediately following standard stimuli. Sleep likewise enhanced the formation of an abstract sequence model, independent of the temporal context during training. Moreover, sleep increased confidence for sequence knowledge, reflecting enhanced metacognitive access to the model. Our results suggest that sleep supports the formation of internal models which can be used to predict upcoming events in different contexts.SIGNIFICANCE STATEMENT To efficiently interact with the ever-changing world, we predict upcoming events based on similar previous experiences. Sleep is known to benefit memory consolidation. However, it is not clear whether sleep specifically supports the transformation of past experience into predictions of future events. Here, we find that, when human subjects sleep after learning a sequence of predictable visual events, they make better predictions about upcoming events compared with subjects who stayed awake for an equivalent period of time. In addition, sleep supports the transfer of such knowledge between different temporal contexts (i.e., when sequences unfold at different speeds). Thus, sleep supports perception and action by enhancing the predictive utility of previous experiences.

Behavioral and electrophysiological responses to fairness norm violations in antisocial offenders.

Antisocial personality disorder is characterized by a stable, lifelong pattern of disregard for and violation of others' rights. Disruptions in the representation of fairness norms may represent a key mechanism in the development and maintenance of this disorder. Here, we investigated fairness norm considerations and reactions to their violations. To examine electrophysiological correlates, we assessed the medial frontal negativity (MFN), an event-related potential previously linked to violations of social expectancy and norms. Incarcerated antisocial violent offenders (AVOs, n = 25) and healthy controls (CTLs, n = 24) acted as proposers in the dictator game (DG) and ultimatum game (UG) and received fair vs. unfair UG offers from either another human (social context) or a computer (non-social context). Results showed that AVOs made lower offers in the DG but not the UG, indicating more rational and strategic behavior. Most importantly, when acting as recipients in the UG, acceptance rates were modulated by social context in CTLs, while AVOs generally accepted more offers. Correspondingly, ERP data indicated pronounced MFN amplitudes following human offers in CTLs, whereas MFN amplitudes in AVOs were generally reduced. The current data suggest intact fairness norm representations but altered reactions to their violation in antisocial personality disorder.

Effects of attentional load on early visual processing depend on stimulus timing.

A growing number of studies suggest that early visual processing is not only affected by low-level perceptual attributes but also by higher order cognitive factors such as attention or emotion. Using high-density electroencephalography, we recently demonstrated that attentional load of a task at fixation reduces the response of primary visual cortex to irrelevant peripheral stimuli, as indexed by the C1 component. In the latter study, peripheral stimuli were always presented during intervals without task-relevant stimuli. Here, we use a similar paradigm but present central task stimuli and irrelevant peripheral stimuli simultaneously while keeping all other stimulus characteristics constant. Results show that rather than to suppress responses to peripheral stimulation, high attentional load elicits higher C1 amplitudes under these conditions. These findings suggest that stimulus timing can profoundly alter the effects of attentional load on the earliest stages of processing in human visual cortex.

Effects of selective attention on the C1 ERP component: A systematic review and meta-analysis.

The C1 event-related potential (ERP) captures the earliest stage of feedforward processing in the primary visual cortex (V1). An ongoing debate is whether top-down selective attention can modulate the C1. One side of the debate pointed out that null findings appear to outnumber positive findings; thus, selective attention does not seem to influence the C1. However, this suggestion is not based on a valid approach to summarizing evidence across studies. Therefore, we conducted a systematic review and meta-analysis investigating the effects of selective attention on the C1, involving 47 experiments and 794 subjects in total. Despite heterogeneity across studies, results suggested that attention has a moderate effect on the C1 (Cohen's d z  = 0.33, p < .0001); that is, C1 amplitude is larger for visual stimuli that are attended than unattended. These results suggest that C1 is affected by top-down selective attention.

Retinotopically specific effects of attention on human early visual cortex activity.

Attention helps us to select what is relevant from the enormous amounts of information taken up by our senses. However, it remains unclear just how early in sensory processing attentional selection can occur. Here, we investigated this question in healthy volunteers by assessing the effect of attentional load on the earliest component (C1) of the visual evoked potential (VEP). We mapped participants' C1 responses to task-irrelevant peripheral textures of different densities and then selected those textures eliciting maximal C1 amplitudes in the upper and lower visual field in each participant. In a second experimental session, these optimal C1 stimuli served as peripheral distracters while participants performed easy or difficult detection tasks at fixation. Our results show a reduction of C1 amplitudes under high attentional load selectively in the lower visual field. This asymmetric effect is opposite to previously reported results obtained without preselecting stimuli. We conclude that attentional selection during early visual processing is possible, but depends on the interaction between anatomic and functional anisotropies of the visual system. This underscores the importance of precisely delineating when, where, and how attentional filtering can operate on initial perceptual processing. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Effects of group affiliation on neural signatures of fairness norm violations in antisocial violent offenders.

While norm-violating behavior in antisocial individuals has been widely studied, little is known about how these people react to unfair behavior directed towards them. Previous research yields inconclusive results with some evidence for rational and strategic behavior in antisocial individuals. Electrophysiological correlates as well as socio-contextual factors such as group affiliation that may inform decision making on fairness considerations have not been investigated in previous studies. This study compared fairness considerations of antisocial violent offenders (N = 25) and controls (N = 26) by using the Ultimatum Game where one player proposes a split of resources and the other player has to respond by accepting or declining the offer. Group affiliation of the proposer (in- vs. out-group) and fairness of offers (fair vs. unfair) were manipulated. We found no difference between groups regarding decision behavior. However, healthy participants showed an electrophysiological response to group affiliation, which was attenuated in the violent offender group. This data suggests intact understanding of social norms in antisocial violent offenders while electrophysiological response pattern may be linked to impaired emotional reactions to expectancy violations.

Occipital sleep spindles predict sequence learning in a visuo-motor task.

STUDY OBJECTIVES: The brain appears to use internal models to successfully interact with its environment via active predictions of future events. Both internal models and the predictions derived from them are based on previous experience. However, it remains unclear how previously encoded information is maintained to support this function, especially in the visual domain. In the present study, we hypothesized that sleep consolidates newly encoded spatio-temporal regularities to improve predictions afterwards. METHODS: We tested this hypothesis using a novel sequence-learning paradigm that aimed to dissociate perceptual from motor learning. We recorded behavioral performance and high-density electroencephalography (EEG) in male human participants during initial training and during testing two days later, following an experimental night of sleep (n = 16, including high-density EEG recordings) or wakefulness (n = 17). RESULTS: Our results show sleep-dependent behavioral improvements correlated with sleep-spindle activity specifically over occipital cortices. Moreover, event-related potential (ERP) responses indicate a shift of attention away from predictable to unpredictable sequences after sleep, consistent with enhanced automaticity in the processing of predictable sequences. CONCLUSIONS: These findings suggest a sleep-dependent improvement in the prediction of visual sequences, likely related to visual cortex reactivation during sleep spindles. Considering that controls in our experiments did not fully exclude oculomotor contributions, future studies will need to address the extent to which these effects depend on purely perceptual versus oculomotor sequence learning.

Binocular disparity-based learning is retinotopically specific and independent of sleep.

Sleep supports the consolidation of recently encoded declarative and procedural memories. An important component of this effect is the repeated reactivation of neuronal ensemble activity elicited during memory encoding. For perceptual learning, however, sleep benefits have only been reported for specific tasks and it is not clear whether sleep targets low-level perceptual, higher-order temporal or attentional aspects of performance. Here, we employed a coarse binocular disparity discrimination task, known to rely on low-level stereoscopic vision. We show that human subjects improve over training and retain the same performance level across a 12-h retention period. Improvements do not generalize to other parts of the visual field and are unaffected by whether the retention period contains sleep or not. These results are compatible with the notion that behavioural improvements in binocular disparity discrimination do not additionally benefit from sleep when compared with the same time spent awake. We hypothesize that this might generalize to other strictly low-level perceptual tasks. This article is part of the Theo Murphy meeting issue 'Memory reactivation: replaying events past, present and future'.

Attentional load modifies early activity in human primary visual cortex.

Recent theories of selective attention assume that the more attention is required by a task, the earlier are irrelevant stimuli filtered during perceptual processing. Previous functional MRI studies have demonstrated that primary visual cortex (V1) activation by peripheral distractors is reduced by higher task difficulty at fixation, but it remains unknown whether such changes affect initial processing in V1 or subsequent feedback. Here we manipulated attentional load at fixation while recording peripheral visual responses with high-density EEG in 28 healthy volunteers, which allowed us to track the exact time course of attention-related effects on V1. Our results show a modulation of the earliest component of the visual evoked potential (C1) as a function of attentional load. Additional topographic and source localization analyses corroborated this finding, with significant load-related differences observed throughout the first 100 ms post-stimulus. However, this effect was observed only when stimuli were presented in the upper visual field (VF), but not for symmetrical positions in the lower VF. Our findings demonstrate early filtering of irrelevant information under increased attentional demands, thus supporting models that assume a flexible mechanism of attentional selection, but reveal important functional asymmetries across the VF.

Effects of perceptual learning on primary visual cortex activity in humans.

Psychophysical and neuroimaging studies suggest that perceptual learning may affect activity in primary visual cortex (V1). Yet, it remains unclear whether such changes involve intrinsic V1 plasticity or feedback from later processing stages. Here we recorded high-density electro-encephalography in 24 volunteers, 24-h after training on a visual texture discrimination task in the upper or lower visual-field. Post-training improvement in upper visual-field was associated with changes in early visual responses, starting 40ms post-stimulus, with reduced amplitude of retinotopic C1, known to reflect V1 activity. No behavioral or neurophysiological effect was found after training in lower visual-field, suggesting retinotopic constraints on perceptual learning. Our results demonstrate that successful acquisition of a perceptual skill can produce long-lasting changes for initial sensory inputs in the adult human visual system.

Modulation of the earliest visual evoked potential by attention: now you see it, now you don't.

Baumgartner and colleagues (this issue) report a replication of an ERP study by Kelly, Gomez-Ramirez, and Foxe (2008). Unlike the original authors, they failed to observe a significant modulation of the C1 by visuo-spatial attention. They conclude that initial afferent processing in V1 is impermeable to visuo-spatial attention. Although their study, like any replication effort, is valuable and important, there are some uncertainties at the methodological and statistical levels suggesting that the absence of evidence is not evidence of absence in the present case.

Early retinotopic responses to violations of emotion-location associations may depend on conscious awareness.

Reports of modulations of early visual processing suggest that retinotopic visual cortex may actively predict upcoming stimuli. We tested this idea by showing healthy human participants images of human faces at fixation, with different emotional expressions predicting stimuli in either the upper or the lower visual field. On infrequent test trials, emotional faces were followed by combined stimulation of upper and lower visual fields, thus violating previously established associations. Results showed no effects of such violations at the level of the retinotopic C1 of the visual evoked potential over the full sample. However, when separating participants who became aware of these associations from those who did not, we observed significant group differences during extrastriate processing of emotional faces, with inverse solution results indicating stronger activity in unaware subjects throughout the ventral visual stream. Moreover, within-group comparisons showed that the same peripheral stimuli elicited differential activity patterns during the C1 interval, depending on which stimulus elements were predictable. This effect was selectively observed in manipulation-aware subjects. Our results provide preliminary evidence for the notion that early visual processing stages implement predictions of upcoming events. They also point to conscious awareness as a moderator of predictive coding.

Distraction by salient stimuli in adults with attention-deficit/hyperactivity disorder: Evidence for the role of task difficulty in bottom-up and top-down processing.

The cognitive mechanisms of increased distractibility in attention-deficit/hyperactivity disorder (ADHD) are poorly understood. The current study investigated the influence of two major modulating factors (emotional saliency, task difficulty) on behavioral and electrophysiological parameters underlying distractibility in ADHD. In addition, the attentional focus (indirect and direct processing of distractors) was examined. Thirty-six adults with ADHD and 37 healthy controls completed two experimental tasks while electroencephalography (EEG) data was collected. Task 1 assessed indirect processing of emotional or neutral distractors during a perceptual judgment task with varying task difficulty. Task 2 measured direct processing of the emotional or neutral stimuli and required participants to rate the stimuli regarding valence and arousal. Results showed that adults with ADHD exhibited generally higher behavioral distractibility than healthy controls. Furthermore, the ADHD group exhibited an enhanced bottom-up processing [increased early posterior negativity (EPN) amplitudes] of distractors in trials with high task difficulty as well as enhanced top-down processing [increased late positive potential (LPP) amplitudes] in trials with low task difficulty. However, no group differences were evident in the neural processing of emotional content or between attentional focus conditions. These findings support the notion that distractibility in ADHD results from impairments to both top-down as well as bottom-up processes and underscore the importance of task difficulty as a modulating factor.

Sleep Supports the Slow Abstraction of Gist from Visual Perceptual Memories.

Sleep benefits the consolidation of individual episodic memories. In the long run, however, it may be more efficient to retain the abstract gist of single, related memories, which can be generalized to similar instances in the future. While episodic memory is enhanced after one night of sleep, effective gist abstraction is thought to require multiple nights. We tested this hypothesis using a visual Deese-Roediger-McDermott paradigm, examining gist abstraction and episodic-like memory consolidation after 20 min, after 10 hours, as well as after one year of retention. While after 10 hours, sleep enhanced episodic-like memory for single items, it did not affect gist abstraction. One year later, however, we found significant gist knowledge only if subjects had slept immediately after encoding, while there was no residual memory for individual items. These findings indicate that sleep after learning strengthens episodic-like memories in the short term and facilitates long-term gist abstraction.

What is Bottom-Up and What is Top-Down in Predictive Coding?

Everyone knows what bottom-up is, and how it is different from top-down. At least one is tempted to think so, given that both terms are ubiquitously used, but only rarely defined in the psychology and neuroscience literature. In this review, we highlight the problems and limitations of our current understanding of bottom-up and top-down processes, and we propose a reformulation of this distinction in terms of predictive coding.

Anger elicitation in tonga and Germany: the impact of culture on cognitive determinants of emotions.

The cognitive appraisal of an event is crucial for the elicitation and differentiation of emotions, and causal attributions are an integral part of this process. In an interdisciplinary project comparing Tonga and Germany, we examined how cultural differences in attribution tendencies affect emotion assessment and elicitation. Data on appraising causality and responsibility and on emotional responses were collected through questionnaires based on experimentally designed vignettes, and were related to culture-specific values, norms, and the prevailing self-concept. The experimental data support our hypothesis that - driven by culturally defined self-concepts and corresponding attribution tendencies - members of the two cultures cognitively appraise events in diverging manners and consequently differ in their emotional responses. Ascription of responsibility to self and/or circumstances, in line with a more interdependent self-concept, co-varies with higher ratings of shame, guilt, and sadness, whereas ascription of responsibility to others, in line with a less interdependent self-concept, co-varies with higher ratings of anger. These findings support the universal contingency hypothesis and help to explain cultural differences in this domain on a fine-grained level.

Using real-time fMRI to learn voluntary regulation of the anterior insula in the presence of threat-related stimuli.

Previous studies have shown that healthy participants learn to control local brain activity with operant training by using real-time functional magnetic resonance imaging (rt-fMRI). Very little data exist, however, on the dynamics of interaction between critical brain regions during rt-fMRI-based training. Here, we examined self-regulation of stimulus-elicited insula activation and performed a psychophysiological interaction (PPI) analysis of real-time self-regulation data. During voluntary up-regulation of the left anterior insula in the presence of threat-related pictures, differential activations were observed in the ventrolateral prefrontal cortex, the frontal operculum, the middle cingulate cortex and the right insula. Down-regulation in comparison to no-regulation revealed additional activations in right superior temporal cortex, right inferior parietal cortex and right middle frontal cortex. There was a significant learning effect over sessions during up-regulation, documented by a significant improvement of anterior insula control over time. Connectivity analysis revealed that successful up-regulation of the activity in left anterior insula while viewing aversive pictures was directly modulated by dorsomedial and ventrolateral prefrontal cortex. Down-regulation of activity was more difficult to achieve and no learning effect was observed. More extensive training might be necessary for successful down-regulation. These findings illustrate the functional interactions between different brain areas during regulation of anterior insula activity in the presence of threat-related stimuli.